Date: Sat, 10 Jan 2009 13:43:35 +0100
From: Ingo Molnar <mingo@elte.hu>
To: =?iso-8859-1?Q?J=F6rn?= Engel <joern@logfs.org>
Cc: David Brown <lkml@davidb.org>, Phil Oester <kernel@linuxace.com>,
       Kay Sievers <kay.sievers@vrfy.org>,
       Phillip Lougher <phillip@lougher.demon.co.uk>,
       Andrew Morton <akpm@linux-foundation.org>,
       Christoph Hellwig <hch@infradead.org>, torvalds@linux-foundation.org,
       linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org
Subject: Re: [GIT PULL] Squashfs pull request for 2.6.29
Message-ID: <20090110124335.GB30744@elte.hu>
References: <E1LKy3v-0003KO-Nx@dylan.lougher.demon.co.uk> <20090108165029.GA10951@infradead.org> <20090108175338.2abbee16.akpm@linux-foundation.org> <4966B24E.1050700@lougher.demon.co.uk> <ac3eb2510901081824g38abc47g4619e80ffaf8f1c5@mail.gmail.com> <20090109023629.GA29520@linuxace.com> <20090109165422.GF24884@logfs.org> <20090109193738.GA9827@linode.davidb.org> <20090109211937.GA14342@logfs.org>
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* J?rn Engel <joern@logfs.org> wrote:

> On Fri, 9 January 2009 11:37:39 -0800, David Brown wrote:
> > On Fri, Jan 09, 2009 at 05:54:22PM +0100, J?rn Engel wrote:
> > >
> > > In general, filesystems and ABI changes are special because stupid 
> > > mistakes are eternal.  If some device driver has a bug, you can fix 
> > > it, reboot and be done with it.  Not so with filesystems.
> > 
> > Squashfs is readonly from the kernel.  The images are created with 
> > userspace tools.
> 
> While true, it doesn't make a difference.  If, for example, your 
> structures members are not naturally aligned, you take a performance hit 
> for no good reason.  Simply moving fields around would make the code go 
> faster.  But the format is fixed and prevents you from making this 
> change.
> 
> You have to get those things right from the beginning or pay for your 
> mistakes everafter.  In general (and I stress "In general") filesystems 
> want more review than ordinary device drivers.  And just to stress that 
> again, this is not an argument against merging squashfs now.

What does a performance hit have to do with an ABI? Absolutely nothing - 
if such a bug is noticed it is fixed, that's it. Your argument does not 
parse and makes absolutely zero technical sense.

Your "ABI is forever" objection against a _read only_ filesystem is a 
newbie mistake worthy of cookie file inclusion - i had a real good laugh 
when i read it ;-)

	Ingo
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